The development of methods to classify or identify bacteria has been an ongoing goal of the microbiology community since the very beginning of the discipline of microbiology. Early methods for classification were based upon microscopic examination of the microorganism and subsequent description of their cell morphology, i.e., coccal shaped cells, rod (bacillus) shaped cells, coccal-bacillus shaped cells, budding yeasts, and sphirochytes. Microbiologists also described their microscopic observations of microorganism cell arrangements as an additional means of categorizing microorganisms, i.e., streptococcus referred to a chain of coccal shaped cells resembling a string of pearls, staphylococcus referred to a cluster of coccal shaped cells resembling a cluster of grapes, etc. Later on stains were developed to add to the differentiating capabilities of the microscope. Far most important of these was the Gram Stain which divided microorganisms into two groups; gram-negative microorganisms, which stain pink to red, and gram-positive organisms, which stained light blue to blue. It was subsequently observed that among microorganisms that cause human disease, most gram-negative microorganisms were rod shaped and most gram-positive microorganisms were coccal shaped. Another early means of differentiating microorganism was to determine the microorganism's ability to grow in the presence or absence of oxygen. Microorganisms which grow in the presence of oxygen are called aerobes and those which grow in the absence of oxygen are called anaerobes.
One of the more important early discoveries in diagnostic microbiology was the ability to grow bacteria in test tubes or in petri plates using different types of liquid or solid bacteriologic growth media. Microbiologists subsequently began to add various chemicals to the growth media to develop further means of differentiating among microorganisms, such as growth or growth inhibition tests, e.g., 6.5% NaCl inhibits the growth of streptococci but not enterococci, or biochemical tests, e.g., enteric bacteria ferment the glucose to produce acid end products while nonfermentative bacteria do not.
The combining of all of the above-mentioned morphological, growth/inhibition, and biochemical tests into a battery of tests available to microbiologists for classifying bacteria led to the development of means of classifying bacteria into the traditional taxanomic entities of family, genus, species used to classify all living things. The microbiologists' approach historically has been to develop batteries of classifying tests which are applicable to only one group or family of microorganisms, e.g., Facklam's scheme for identifying viridans streptococci (Ref. 3), Kloos and Schleifer's scheme for identifying coagulase-negative staphylococci (Ref. 2), Edwards and Ewing scheme for identifying gram-negative enterics (Ref. 1), etc. Each of these schemes uses test formulations that were designed especially for the metabolism and growth characteristics of the family of microorganisms the scheme addresses. Thus, a glucose fermentation test for streptococci is formulated differently than a glucose fermentation test for staphylococci and for enteric microorganisms. In fact, commercial suppliers of prepared bacteriologic media provide the above family-specific formulations on a commercial basis. The Remel (12076 Santa Fe Drive, Lenexa, Kan. 66215-3594) Catalog No. 103 (January 1994) offers microbiologists a wide variety of conventional tubed biochemical formulations with which to perform the above referenced identification schemes. The Remel catalog specifically offers eight (8) different formulations of media for detecting carbohydrate fermentation by seven (7) different families of microorganisms. They are as follows: Purple Broth is used for testing enterics (see pages 40-41), Phenol Red Broth is used for testing Streptococci (see pages 38-39), P.R.A.S. Medium and CHO Medium are used to test Anaerobes (see pages 29-30, and 40), CTA Medium and Heart Infusion Broth are used to test Fastidious microorganisms (see pages 30-31, and 33), OF Medium is used for testing Nonfermentative Gram-negative bacilli and enterics (see pages 37-38), and Yeast Fermentation Broth is used for testing Yeast (see pages 47-48).
References:
1. Ewing, W. H., 1986, "Edwards and Ewing's Identification of Enterobacteriaceae", 4th ed., Elsevier Science Publishing Co., New York. PA0 2. Kloose, W. E., and K. H. Schleifer, 1975, "Simplified scheme for routine identification of human Staphylococcus species", J. Clin. Microbiol., 1:82-88. PA0 3. Facklam, R. R., and J. A. Washington II, 1991, "Streptococcus and related catalase-negative gram-positive cocci", p. 238-257, In A. Barlows, W. J. Hausler, Jr., K. L. Herrmann, H. D. Isenberg, and H. J. Shadome (ed.), Manual of Clinical Microbiology, 5th ed., American Society for Microbiology, Washington, D.C.
Beginning in the late 1960's with Roche Diagnostic's (1447 York Court, Burlington, N.C. 27215) introduction of the Enterotube Identification system for enteric bacteria and followed quickly by API's (595 Anglum Drive, Hazelwood, Mo. 63042-2395) release of the 20E Enteric Identification System, diagnostic companies began to adopt this same rationale for the development and manufacture of commercial bacterial identification kits. Vitek, MicroScan, IDS (Innovative Diagnostic Systems, 2797 Peterson Place, Norcross, Ga. 30071), and API each offer a family-specific product to identify each family or group of bacteria. (See Table I below).
TABLE I ______________________________________ Micro- organism MicroScan IDS Vitek API ______________________________________ Entero- MicroScan Dry IDS RapID Vitek API 20E bacteriaceae Overnight Gram- onE GNI negative ID Panel card Staphylococci MicroScan Vitek API Overnight GPI Staphldent; Dry Gram-positive card API ID panel UniScept 20GP; APISTAPH Streptococci MicroScan IDS RapID Vitek API 20S; Overnight STR GPI API Dry Gram-positive card UniScept ID panel 20GP Anaerobe MicroScan Rapid IDS RapID API 20A; Anaerobe Panel Ana API Anldent Yeast MicroScan Rapid IDS RapID Vitek API 20C Yeast ID Panel Yeast Panel YBC card Fastidious MicroScan HNID IDS RapID Vitek API NH NHI QuadFerm ______________________________________
History has taught microbiologists that the identification of clinical isolates or strains of microorganisms belonging to different families of bacteria requires the use of different conventional tube biochemical schemes or different commercial products. All traditional biochemical tests rely on growth as a means of amplifying the number of cells and inducing certain enzymes. The need to optimize the test formulae to the growth characteristics of individual families of bacteria is the basis for the historical focus on family specific tests (traditional tubed biochemical or commercial kits). For example, in the above discussion of conventional biochemical tests, there are eight different formulations for glucose fermentation formulated to be specifically reactive with seven different families of microorganisms. Because conventional biochemical tests are for the most part growth dependent, each glucose fermentation reaction has been optimized for growth of a particular family of microorganisms and for detection of glucose fermentation by that family of microorganism. This practice was carried forward by commercial biochemical identification systems, in that there are different biochemical identification products (see above list) for each of the different families or groups of microorganisms. The development of group specific product classes is both a reflection of the need to develop formulations to support family or group specific growth characteristics and to optimize substrate reactivity for the metabolism of each family or group of microorganisms. When diagnostic companies began the development of rapid identification tests that utilized chromogenic, fluorogenic or rapid conventional tests detected calorimetrically or fluorometrically, the family specific product format continued, even though the dependence on growth was greatly diminished. These new rapid ID systems were growth independent rather than growth dependent. They assay for preformed enzymes present in denser suspensions of bacteria than were used in growth-based systems.
Accordingly, it would be desirable to have a universal test system to classify and/or identify a microorganism belonging to one of any number of divergent multiple groups of microorganisms, such as by using a single battery of biochemical tests, thus, avoiding use of multiple batteries of tests or commercial test kits wherein each test battery or combination is tailored to specific groups or families of microorganisms.